1. Technical Field
The present invention relates to a hologram recording method, a hologram recording device, a hologram playback method, and an optical recording medium. In particular, the present invention relates to a hologram recording method and device which illuminate signal light and reference light coaxially onto a reflecting-type optical recording medium and record a hologram, a hologram playback method which plays-back a hologram recorded by this method, and an optical recording medium used in recording a hologram by this method.
2. Related Art
A method has been proposed of manufacturing a transmitting-type hologram by illuminating signal light and reference light coaxially from the same surface side of a recording medium. In this method, signal light and reference light, which are generated from spatially different positions of a spatial light modulator, are Fourier-transformed by a lens. Because the Fourier-transformed signal light and reference light overlap in a vicinity of the Fourier transform plane, a hologram can be recorded by placing a recording medium at that position. Further, in this method, because the signal light and the reference light are illuminated coaxially, the optical system is simple, and the recording device can be made to be compact.
However, coaxial recording of a transmitting-type hologram has the problem that the spatial overlapping of the signal light and the reference light is small. In particular, if the film thickness of the recording material is large, there is the problem that, the further away from the Fourier transform plane in the optical axis direction, the smaller the region where the signal light and the reference light overlap, and a hologram cannot be recorded in the entire optical axis direction (thickness direction) of the recording material.